Poly(alkylene terephthalate) resins are used for manufacturing fibers, films, and molded articles and have excellent physical properties such as high wear resistance, durability, and heat resistance.
An important class of poly(alkylene terephthalate) resins are the PCT resins based on reactions between 1,4-cyclohexanedimethanol and terephthalic acid or suitable synthetic equivalents. Glass fiber reinforced PCT compositions having high crystallinity have excellent properties with regard to strength, stiffness, and heat resistance. These PCT compositions are useful in applications where high strength, stiffness, and heat resistance are necessary, for example, molded parts for use in the automotive and electronic industries.
High crystallinity is essential to ensure adequate hardness, strength, and heat resistance at elevated temperatures. To ensure adequate crystallinity, PCT compositions generally require mold temperatures of 150.degree. C. or higher. High mold temperatures are possible only with sophisticated molding equipment and require specialized heating means, such as, for example, oil bath heating units. Such units are expensive to purchase and to operate.
Crystallization aids have been suggested as a method of promoting crystallization in poly(alkylene terephthalate) at lower temperatures to lower the required mold temperature. The use of ester compounds as crystallization aids is described, for example, in U.S. Pat. Nos. 4,223,125 and 4,223,113. Certain amides are mentioned as a component in crystallization systems for poly(ethylene terephthalate) in U.S. Pat. Nos. 4,351,757 and 4,352,904. Other types of crystallization aids include ketones and sulfonamides. However, these additives can be volatile at high temperatures giving rise to volatility losses of the additives during drying which result in difficulties in drying the PCT compositions after compounding.
Accordingly, a need remains for glass fiber reinforced PCT compositions which can be molded at low temperatures and yet retain adequate physical properties.